The use of intravascular medical devices has become an effective method for treating many types of vascular disease. In general, a suitable intravascular medical device is inserted into the vascular system of the patient and navigated through the vasculature to a desired target site. Catheters and guidewires are often utilized to place intravascular medical devices such as stents and embolic devices at desired locations within the patient's body.
Intravascular catheters are currently utilized in a wide variety of minimally invasive medical procedures. Generally, an intravascular catheter enables a physician to remotely perform a medical procedure by inserting the catheter into the vascular system of the patient at a location that is easily accessible and thereafter navigating the catheter to the desired target site. By this method, virtually any target site in the patient's vascular system may be remotely accessed, including the coronary, cerebral, and peripheral vasculature.
Typically, the catheter enters the patient's vasculature at a convenient location such as a blood vessel in the neck or near the groin. Once the distal portion of the catheter has entered the patient's vascular system, the physician may urge the distal tip forward by applying longitudinal forces to the proximal portion of the catheter. For the catheter to effectively communicate these longitudinal forces, it is desirable for the catheter to have a high level of pushability and hoop strength, which confers kink and ovalization resistance.
Frequently, the path taken by a catheter through the vascular system is tortuous, requiring the catheter to change direction frequently. It may also be necessary for the catheter to double back on itself. Physicians often apply torsional forces to the proximal portion of the catheter to aid in steering the catheter. To facilitate the steering process, it is desirable that an intravascular catheter have a relatively high level of torqueability. Furthermore, in order for the catheter to conform to a patient's tortuous vascular system, it is desirable that intravascular catheters be very flexible.
The distance between the access site and the target site is often in excess of 100 cm. The inside diameter of the vasculature at the access site is often less than 5 mm. In light of the geometry of the patient's body, it is desirable to combine the features of torqueability, pushability, and flexibility into a catheter which is relatively long and has a relatively small diameter.
Ideally, the distal end of an intravascular catheter will be adapted to reduce the probability that the vascular tissue will be damaged as the catheter is progressed through the vascular system. This is sometimes accomplished by bonding or welding a relatively soft tip member to the distal end of an intravascular catheter.
After the intravascular catheter has been navigated through the patient's vascular system so that its distal end is adjacent the target site, the catheter may be used for various diagnostic and/or therapeutic purposes. One example of a diagnostic use for an intravascular catheter is the delivery of radiopaque contrast solution to enhance fluoroscopic visualization. In this application, the intravascular catheter provides a fluid path leading from a location outside the body to a desired location inside the body of a patient. In order to maintain a fluid path, it is desirable that intravascular catheters be sufficiently resistant to kinking and ovalization. These qualities can be secured through increased hoop strength. In addition, because such fluids are delivered under pressure, it is also desirable that intravascular catheters be sufficiently resistant to bursting or leaking.
One useful therapeutic application of intravascular catheters is the treatment of intracranial aneurysms in the brain. Approximately 25,000 intracranial aneurysms rupture each year in North America. An aneurysm which is likely to rupture, or one which has already ruptured, may be treated by delivering an embolic device or agent to the interior of the aneurysm. The embolic device or agent encourages the formation of a thrombus inside the aneurysm. The formation of a thrombus reduces the probability that an aneurysm will rupture. The formation of a thrombus also reduces the probability that a previously ruptured aneurysm will re-bleed. Thrombus agents which may be used include liquid thrombus agents such as cyanoacrylate, and granulated thrombus agents such as polyvinyl alcohol. An additional type of thrombus agent which is frequently used is a tiny coil. Any of the thrombus agents described above may be delivered using an intravascular catheter.
When treating an aneurysm with the aid of an intravascular catheter, the catheter tip is typically positioned proximate the aneurysm site. The thrombus agent is then urged through the lumen of the intravascular catheter and introduced into the aneurysm. Shortly after the thrombus agent is placed in the aneurysm, a thrombus forms in the aneurysm and is shortly thereafter complemented with a collagenous material which significantly lessens the potential for aneurysm rupture. It is desirable that the lumen of the catheter provides a path for delivering embolic devices to an aneurysm. To this end, it is desirable that the pathway through the catheter have a low friction surface.
The blood vessels in the brain frequently have an inside diameter of less than 3 mm. Accordingly, it is desirable that intravascular catheters intended for use in these blood vessels have an outside diameter which allows the catheter to be easily accommodated by the blood vessel. The path of the vasculature inside the brain is highly tortuous, and the blood vessels are relatively fragile. Accordingly, it is desirable that distal portion of a catheter for use in the brain be adapted to follow the highly torturous path of the neurological vasculature.
As described above, it is desirable to combine a number of performance features in an intravascular catheter. It is desirable that the catheter have a relatively high level of pushability and torqueability, particularly near its proximal end. It is also desirable that a catheter be relatively flexible, particularly near its distal end. The need for this combination of performance features is sometimes addressed by building a catheter which has two or more discrete tubular members having different performance characteristics. For example, a relatively flexible distal section may be bonded to a relatively rigid proximal section. When a catheter is formed from two or more discrete tubular members, it is necessary to form a bond between the distal end of one tubular member and the proximal end of another tubular member.
These catheters are designed to be used with a guidewire. A guidewire is simply a wire, typically of very sophisticated design, which is the “scout” for the catheter. The catheter fits over and slides along the guidewire as it passes through the vasculature. Said another way, the guidewire is used to select the proper path through the vasculature with the urging of the attending physician and the catheter slides along behind once the proper path is established. There are other ways of causing a catheter to proceed through the human vasculature to a selected site, but a guidewire-aided catheter is considered to be both quite quick and somewhat more accurate than the other procedures. Because guidewires navigate the same tortuous paths as intravascular catheters, it is also desirable that guidewires have relatively high levels of hoop strength, pushability, and torqueability.